Fluorescent lamps are used in a variety of applications, such as for general purpose lighting in commercial and residential locations, in backlights for liquid crystal displays in computers and televisions, etc. Fluorescent lamps generally include a glass tube, circle, spiral or other shaped bulb containing a gas at low pressure, such as argon, xenon, neon, or krypton, along with low pressure mercury vapor. A fluorescent coating is deposited on the inside of the lamp. As an electrical current is passed through the lamp, mercury atoms are excited and photons are released, most having frequencies in the ultraviolet spectrum. These photons are absorbed by the fluorescent coating, causing it to emit light at visible frequencies.
A number of different types of fluorescent lamps exist, such as cold cathode fluorescent lamps (CCFLs) and compact fluorescent lamps (CFLs), traditional full size fluorescent lamps, etc. In general, the various types of fluorescent lamps share a requirement for a high voltage current-limited AC power supply. A very high voltage is initially applied to strike or light the lamp. Once the lamp is lit, the electrical resistance in the lamp drops and the voltage is reduced to avoid high currents. As current passes through the fluorescent lamp, the electrical resistance of the lamp drops, allowing more current to flow. Traditionally, relatively expensive and bulky ballasts are used to limit the current through the fluorescent lamp, as well as to provide the voltage needed to strike the lamp. However, traditional fluorescent lamp ballasts, in addition to being relatively expensive and bulky, can be noisy and prone to failure, and are not dimmable using TRIAC-based dimmers. Often, for low power and self ballasting applications including CFLs, traditional ballasts have electrical characteristics that are undesirable including low power factor values and performance.